When manufacturing a laminate such as a printed circuit board, the following method is used in a press-forming or thermocompression bonding process. As shown in FIG. 16, a laminate material 112, which is an object to be pressed, is placed between heating platens 113 serving as heating and pressing means and a certain pressure and temperature are applied to the laminate material 112. In order to produce a formed product with high precision, it is necessary to uniformly heat and press the entire surface of the laminate material 112 in hot press. For this purpose, the hot press is performed with a flat plate-like cushioning material 111 interposed between each heating platen 113 and the laminate material 112.
Conventionally, a paper cushioning material such as kraft paper, a felt cushioning material, etc. is used as such a hot press cushioning material 111. Paper cushioning materials are inexpensive and have cushioning properties. However, the paper cushioning materials cannot be restored after pressing and therefore cannot be repeatedly used for a plurality of presses. Moreover, if the paper cushioning materials are used at high temperatures (e.g., 200° C. or higher), they get burnt and stuck on the heating platens 113, producing paper dust.
Felt cushioning materials are flexible and therefore have cushioning properties. However, the felt cushioning materials, due to their poor temporal stability, cannot uniformly transmit the heat and the pressure from the heating platens 113 to the laminate material 112 across the entire pressing surface after repeated use. Repeated use of the felt cushioning materials therefore produces defective pressed products and also causes fibers to coming off from the surfaces of the felt cushioning materials.
Japanese Patent Nos. 4746523 (Patent Literature 1), 5341733 (Patent Literature 2), 4183558 (Patent Literature 3), etc. propose a hot press cushioning material that can be repeatedly used for high temperature press.
Patent Literature 1 discloses a hot press cushioning material that includes a fiber-rubber composite material layer made of a woven fabric and rubber with which the woven fabric has been impregnated. Bulky yarn made of glass fiber is used as at least one of warp and weft of the woven fabric, and the fiber-rubber composite material layer has voids therein. Patent Literature 2 discloses a hot press cushioning material that includes a surface layer material placed in its surface layer. The surface layer material is formed by a woven fabric layer comprised of bulky yarn, a resin layer covering one surface of the woven fabric layer, and a rubber layer covering the other surface of the woven fabric layer. The woven fabric layer has a woven fabric-resin composite layer and a woven fabric-rubber composite layer and has voids therein. Patent Literature 3 discloses a hot press cushioning material that includes a base material and a releasable coating film formed on the base material and made of a resin composition. The releasable coating film contains a base material comprised of a predetermined resin, and organic powder and inorganic powder which are mixed with the base material.